Embodiments disclosed herein relate generally to micro-valves, to processes for making such and to micro-fluidic devices using such.
Since the first integrated circuit, invented in 1958, miniaturization has become an important research topic in both electronic and non-electronic devices. In the late 1970s, miniaturization was extended to mechanical devices with electronics, which are now known as micro-electro-mechanical systems (MEMS), which have become increasingly popular. The miniaturization of analysis systems has appeared to have a great potential in a broad range of fields, from biomedical to space exploration. Indeed, MEMS enables one to not only minimize the costs of fabrication, but also to reduce the device power and fluid consumptions. Consequently, these systems have been reduced in size to micro scale for the realization of fully integrated micro-fluidic systems, such as lab-on-chip (LOC), micro-total analysis systems (μTAS) using gas/liquid sample injectors, mixers, micro-pumps and compressors.
Micro-valves constitute a basic micro-fluidic element: they are basic components of micro-fluidic systems and permit fluid transfer, switching and control. They are generally used in the fields of gas or liquid chromatography, fluids and pneumatics for controlling the flow of gases and liquids, i.e. fluid flows. MEMS technology has provided an opportunity for micro-valves to be packaged onto a fluidic board with integrated fluidic channels to interconnect all the parts. This is an arrangement similar to a printed circuit board in electronics. From the first pneumatic valves developed for gas flow control in the 1970s to their successful integration into large scale integrated fluidic systems, micro-valves, including their membranes, were mostly manufactured using silicon or metal. Such membranes are relatively simple to process using known etching techniques. For example, an article from A. Luque et al. (Sensors and Actuators, A 118 (2005) 144-151) discloses micro-valves comprising a polysilicon/silicon nitride membrane. However, the resulting devices are highly prone to leaking at ambient temperature due to the rigidity of silicon or metal-based materials.
Recent new developments used alternative materials such as polymers and elastomers. Common polymers used in micro-fabrication include polydimethylsiloxanes (PDMS) or polyimides. For example, an article from J C Galas et al. (Microelectronic Engineering, 78-79 (2005) 112-117) and an article from G. Thuillier (Microsyst Technol (2005) 12: 180-185) disclose micro-valves comprising a PDMS actuation membrane. However, the use of such polymers as PDMS results in non-negligible leaking devices when used with gas because of their porosity. Furthermore, such polymers are not aimed to be used in highly corrosive environments. For example, in gas processing systems, such polymers would likely deteriorate since such materials are not chemically inert to corrosive components such as hydrogen sulfide, thereby altering the quality and reproducibility of the analysis.
From a practical standpoint, the successful miniaturization and commercialization of fully integrated micro-fluidic systems have been delayed due to the lack of reliable micro-fluidic components, i.e., micro-pumps and micro-valves. See Kwang W Oh et al. (A Review of Microvalves, J. Micromech. Microeng. 16 (2006) R13-R39).
In the context of miniaturized sensors involving MEMS, it would be desirable to have a reliable non-leaking micro-valve that may be used in various environments, such as in boreholes, and which is chemically inert and which may be used in a wide range of working temperatures.